U.S. patent number 4,316,233 [Application Number 06/116,498] was granted by the patent office on 1982-02-16 for single phase electrohydrodynamic pump.
Invention is credited to John C. Chato, Joseph M. Crowley.
United States Patent |
4,316,233 |
Chato , et al. |
February 16, 1982 |
Single phase electrohydrodynamic pump
Abstract
Apparatus for pumping charged fluid or charged particles by
means of a travelling electric field which acts on the charge
through Coulombic forces. The electric field is produced by a
single phase time varying voltage applied to material with
dimensions or electrical properties which vary in space. This
material is placed between the medium to be pumped and an
electrical conductor attached to the voltage supply.
Inventors: |
Chato; John C. (Urbana, IL),
Crowley; Joseph M. (Champaign, IL) |
Family
ID: |
22367520 |
Appl.
No.: |
06/116,498 |
Filed: |
January 29, 1980 |
Current U.S.
Class: |
361/233;
417/48 |
Current CPC
Class: |
H02N
11/006 (20130101); B65G 54/02 (20130101) |
Current International
Class: |
B65G
54/00 (20060101); B65G 54/02 (20060101); H02N
11/00 (20060101); B05B 005/02 () |
Field of
Search: |
;361/233,227,228
;417/48,49 ;310/308,309 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Moose, Jr.; Harry E.
Claims
What is claimed is:
1. An apparatus for inducing pumping of a charged medium, said
apparatus consisting of an electrically conducting electrode
connected to a souce of varying voltage, and separated at least
partially from said medium by a non-uniform semi-insulating
covering arranged so that the electrical relaxation time of said
covering increases from lower to higher values over some finite
section of said covering in such a way as to set up a travelling
electric field which exerts a Coulombic force on said medium.
2. An apparatus as in claim 1 and in which said covering is
arranged along the outer surface of said conducting electrode.
3. An apparatus as in claim 1 and in which said covering is
arranged along the inner surface of said conducting electrode.
4. An apparatus as in claim 1 and in which said medium is charged
by the action of said travelling electric field.
5. An apparatus as in claim 1 and in which said medium is charged
by charges injected into said medium by external generation.
6. An apparatus as in claim 1 and in which said variation in
electrical relaxation time is produced by means of geometrical
variation of thickness of the said covering.
7. An apparatus as in claim 1 and in which said variation in
electrical relaxation time is produced by means of variation in the
electrical conductivity of the said covering.
8. An apparatus as in claim 1 and in which said electrode is a wire
introduced into a pipe.
Description
FIELD OF INVENTION
The present invention relates to pumps. More specifically, it
pertains to efficient pumps having no moving parts, and which
utilize alternating electric fields to propel material in a desired
direction.
DISCUSSION OF PRIOR ART
Many mechanical pumps have been developed to move fluids through
pipes. In general, these pumps raise the pressure at the inlet of
the pipe to a value large enough overcome the viscous losses
entailed in moving the fluid through the pipe at the desired flow
rate. As a consequence of this approach, the static pressure at the
inlet region of the pipe is larger than that at the exit.
In many pumping applications, this excess pressure is a distinct
drawback. In the pipes which contain underground electric power
cables, for example, it may be necessary to circulate insulating
oil through the pipe to cool the cables. In order to prevent
electrical breakdown, this oil must be kept under a minimum
pressure, and the excess pressure implied by mechanical pumping
through a long pipe can raise the total pressure above the rating
of the pipe, leading to leaking of the oil or rupture of the
pipe.
One way to avoid this pressure buildup is to use an
electrohydrodynamic pump instead of a mechanical pump. An
electrohydrodynamic pump applies electrostatic forces to charges
inside the medium to be pumped, so as to pull or push the charges
(and attached medium) in the direction of the electric field. Since
the electric force acts directly on the fluid, there is no need to
build up a large pressure, and the problems associated with
pressure buildup in a long pipe can be avoided.
In the prior art (see for example U.S. Pat. Nos. 3,463,944 or
3,778,678), insulating fluids or charged particles have been
propelled by alternating electric fields whose principal component
is a travelling wave which acts either to attract the material in
the direction of travel, or to repel the material in the opposite
direction. In these pumps, the travelling wave was provided by
multiple electrodes connected to an alternating voltage source
providing at least three phases. In many applications, such as the
pumping of fluid through long pipes, the multiple electrodes and
phases require a complicated and expensive structure which
precludes the use of electrohydrodynamic pumping.
These structures could be considerably simplified if only a single
conductor were needed to excite the electrohydrodynamic pump, but
in the prior art, a single phase conductor could not be made to
pump reliably, since the flow might start in either direction, and
might also flow in circular patterns rather than in the desired
direction when the pump is started.
OBJECTS OF THE INVENTION
Accordingly, the principal object of this invention is to provide a
pump for insulating fluids or charged particles which requires only
a single continuous electrode driven by a single phase voltage
supply.
Another object of this invention is to create a travelling
electrostatic wave using only a single phase voltage supply.
A further object of our invention is provide a self-starting
electrohydrodynamic pump.
Yet another object of our invention is to provide a pump having no
moving parts, which is suitable for pumping insulating fluids or
charged particles through long pipes without increasing the
pressure within said pipes.
These and other objects will become evident in the description to
follow and will be particularly pointed out in the appended
claims.
GENERAL DESCRIPTION OF THE OPERATION
Broadly, and by way of summary, the invention relates to an
apparatus adapted to effect pumping of a charged fluid or charged
particles by means of the attractive or repulsive forces exerted on
the charges by an electric field. These forces are due to solely to
the Coulombic interaction, and are not related to the forces
developed on moving charges or currents in a magnetic field (the
dynamoelectric force). In addition, the electric forces act
directly on the material, and not through the intermediary of
mechanical pressure, so that the static pressure inside the
container need not be increased as a result of the pumping.
According to the present invention, the desired objects can be
accomplished by surrounding a single electrically conducting
electrode with a semi-insulating material in which the electrical
properties or geometrical dimensions vary in the direction of
desired motion. This variation is arranged so that when a voltage
is first applied to the electrode, the electric potential at the
surface of the semi-insulating coating will start to rise in
response to the applied excitation. Since the electrical properties
or dimensions vary throughout the coating, however, the rise at the
surface will not be uniformly fast. The regions which have a
relatively short electrical relaxation time will exhibit the
fastest rise, so that the potential there will approach its peak
faster. Later, the regions with intermediate electrical relaxation
times will exhibit voltages near the peak, and finally those
regions with the longest relaxation times will begin to approach
the peak.
If the various regions of the coating are arranged so that the
electrical relaxation times of the material go from the shortest to
the longest value sequentially along the surface of the coating in
some section then the potential at the surface will appear to move
along like a wave as the applied voltage is alternately increased
and decreased. If there are electric charges present in the
adjacent medium, either as charged particles or as space charge
inside a fluid, these charges will be acted on by the Coulomb force
of the electrostatic field, and caused to move either in the
direction of the variation of the electrical relaxation time of the
material or in the opposite direction, according to the sign of the
charge. The sections may be repeated indefinitely, if desired, to
extend the pumping action. This is especially advantageous when
pumping in a long pipe without pressure increases.
FIGURES
In order to facilitate the description and understanding of this
invention, reference is made to the appended drawings, in
which:
FIG. 1 is a drawing of one particular embodiment, in which the
travelling wave is produced by the variation in electrical
conductivity of neighboring projections from the conductor;
FIG. 2 is a representation of the voltages appearing at the ends of
the projections of FIG. 1 in response to a sinusoidal voltage
applied to the conductor;
FIG. 3 is a plot of the position of the peak of the electric
potential wave produced by the structure of FIG. 1;
FIG. 4 is a sketch of an embodiment in which the travelling wave is
induced by variation of the length of the projection.
FIG. 5 is a sketch of an embodiment in which the various
projections are in contact with each other;
FIG. 6 is a sketch of an embodiment in which there is a continuous
variation in the thickness of the covering arranged so as to
produce a travelling wave.
FIG. 7 is a sketch of an embodiment in which the electrical
conductor is a wire and the travelling wave is produced by a
structure attached to the surface of the wire;
FIG. 8 depicts an embodiment in which the different thicknesses are
produced by wrapping a central conductor spirally with material so
as to produce an appropriate variation in thickness.
DESCRIPTION AND OPERATION
Turning now to FIG. 1, we discuss a particular embodiment of the
invention which is most suitable for an explanation of those
features of the present invention which are responsible for the
production of the travelling wave. The invention, shown in a cross
sectional view along the direction of intended motion, includes an
elongated conductor #10 attached to a source of single phase, time
varying voltage #16. Along the conductor #10 are spaced projections
composed of semi-insulating material #11-13. These projections are
of at least three different types of material with differing
electrical conductivity so that the electric relaxation time of
projection #11 is faster than the electrical relaxation time of
projection #12 which in turn is faster than that of projection #13.
The conductor #10 and the projections #11-13 are in contact with
the insulating medium #14 which is to be pumped. Some distance away
from the projections is a ground electrode #15 which is attached to
the opposite polarity of the voltage source #16.
By way of example of the operation of the pump shown in FIG. 1, we
can assume that a sinusoidal voltage is supplied by the source #16
to the conductor #10. Since the medium to be pumped is not a
perfect conductor, the voltage at the tip of the projections would
eventually approach some fraction of the voltage applied by the
source #16 to the conductor #10. Due to the finite relaxation time
of the semi-insulating material, however, the approach to the full
voltage is delayed by an amount which depends on the electrical
relaxation time of the projections and the medium.
For the particular choice of relaxation times associated with FIG.
1, the voltages at the tip of projections #11-13 are shown in FIG.
2. Since the material of projection #11 has the shortest electrical
relaxation time, the voltage #17 at its tip approaches the applied
voltage quickly, and this voltage is very similar to the applied
voltage in magnitude and phase. Turning to projection #12 which has
an longer relaxation time, we find that the voltage #18 at its tip
lags the applied sinusoidal voltage, and is usually reduced in
amplitude. For projection #13 which has the longest electrical
relaxation time, the voltage #19 lags even farther behind the
applied voltage, and has the smallest amplitude.
The effect of these time lags on the positions of maximum voltage
applied to the medium to be pumped is indicated in FIG. 3. This
figure shows the projections #11-13 distributed along the x-axis
#20. The vertical axis #21 represents time. When the peak value of
the electric potential within one section of the structure occurs
at a certain projection, that section is indicated in the graph by
a solid line #22 drawn above that section. The figure shows that
the position of this peak appears to move along the structure in
the x-direction corresponding to a travelling wave of electric
potential. The voltages at the tips of the projections cause an
electric field inside the medium #14 which is to be pumped, and
this electric field acts on the charges #23 inside the medium, thus
pumping them in the desired direction.
Although the time lags needed to produce the travelling wave were
provided by variations in the electrical conductivity of the
various projections in the above embodiment, they can also be
provided by variations in the physical dimensions of the
projections, as shown in FIG. 4. Here, the pump apparatus consists
of a conductor #10 connected to a time-varying voltage source #16,
as in the embodiment of FIG. 1. In the present case, however, the
projections are all made of the same material, so that all
projections have the same electrical conductivity. The various
projections have different dimensions, however, so that projection
#24 is substantially shorter than projection #25 which is in turn
substantially shorter than projection #26. When voltage is applied
to the conductor #10 the voltages at the tips of the projections
will all rise toward the applied voltage, but at different rates,
due to the differences in geometry. Thus, the voltage at the tip of
the shortest projection, #24 will quickly approach the applied
voltage, since its total resistance is least, and also because the
separation from the ground electrode #15 is greatest so that the
capacitance there is least. At the intermediate projection #25 the
voltage at the tip will lag somewhat, due to the increased
resistance associated with the extra length. Finally, the voltage
at the tip of the longest projection #26 will exhibit the greatest
lag, due to the large resistance associated with the long length.
Thus this structure will also produce a travelling wave of electric
potential at the outer surfaces of the projections, just as in the
previous embodiment, and this wave will have the same effect,
namely, the pumping of the insulating medium and the associated
charges.
The previous figures have shown the pump as composed of a series of
discrete projections from the conductor. This was done primarily to
aid in the description of the operation of the invention, and is
not necessary for its successful application. For example, the
semi-insulating projections introduced in FIG. 1 can be made
contiguous, as shown in FIG. 5.
Also, more than three different materials or lengths can be used in
each section, or the material can show a continuous variation of
electrical properties or dimensions throughout the section. This
last possibility is shown in FIG. 6, in which a semi-insulating
material #27 of varying thickness is applied to the conductor #10.
If the thickness increases gradually throughout most of the
section, followed by a more rapid decrease, a travelling wave of
electric potential will still be produced at the surface of the
semi-insulator, and the pump will operate as before.
Likewise, the pump will operate as before in any geometrical
arrangement which includes a good conductor in contact with the
proper semi-insulating materials adjacent to the medium to be
pumped. For instance, the conductor could be a wire, as in FIG. 7.
In this figure, the conductor #10 is surrounded by a
semi-insulating coating which has three different materials #11-13
in a section of the covering, and this section may be repeated
along the length of the wire.
In another variation on the basic pumping apparatus, the change in
electrical properties in the desired direction of pumping can be
achieved by successive wrapping of the conductor, as shown in FIG.
8. This figure again shows a pumping structure arranged around a
central wire #30 which is first entirely surrounded by a
semi-insulating coating #31. This structure is then wrapped with a
tape of semi-insulating material #32 so as to leave a spiral strip
of the first coating #31 uncovered. Lastly, a second
semi-insulating tape #33 is wrapped around the structure so as to
partially cover the first tape #32 leaving one side of the first
tape exposed. This procedure yields a structure similar to that of
FIG. 4 in which a travelling wave is produced by variations in
thickness of the semi-insulating covering. In this case the wave
will travel spirally down the structure, so that there will be a
component which pumps axially, and a second component which pumps
azimuthally, which may be advantageous in some applications. All of
these structures can be extended by repetition of the basic
sectional unit, so as to pump fluid through long pipes. Since the
force is applied directly to the fluid, this extension will not
imply a large pressure head.
This invention has been disclosed in connection with a constant
direction of pumping, but other directions may be used as well. For
example, the method disclosed may be used to circulate materials to
aid in mixing or heat transfer, and the semi-insulating sections
could then be arranged in a circle along some plane in the
container.
Also, the sinusoidal voltage source could be replaced with other
time varying sources which might be more convenient in a particular
application. A square wave of voltage, for example, is simpler to
generate than a sine wave, and might be used in applications which
can not make use of a convenient source of AC power.
These and other modifications of the invention will occur to those
skilled in the art and all such modifications are considered to be
within the spirit and scope of the invention as defined in the
appended claims.
* * * * *